Ultra-high-frequency radio transmitter



Jan. 24, 1939. F. A. KOL STER ET AL I ULTRA'HIGH-FREQUENCY RADIO TRANSMITTER Filed May 11, 1955 4 Sheets-Sheet 1 I 0 o 0 o o o 4 I air/$45722 48 l 2/ I 43' -/9 4 l MHH VOL TAGE MUL T/PZ IE I A romvry Jan. 24, 1939'. F. A. KOLSTER ET AL ULTRAHJTGHFREQUENCY RADIO TRANSMITTER Filed Ma 11, 1955 4 Sheets-Sheet 2 66 94 lure-Mons.- Insulation Minn/(5 4. lrozsrm PAl/l E 870M! y TTORNEY Jan. 24, 1939.,

'F. A. KOLSTER ET AL 2,145,225 ULTR'A-H-IGH-FHEQUENCY RADIO TRANSMITTER Filed May 11, 1935 4 Sheets-Sheet 4 INVE'IUTDRS: FREDERICK 11. KOLSTH! '1 Patented Jan. 24, 1939 UNETED STATES PATENT OFFICE ULTRA-HIGH-FREQUENCY RADIO TRANSMITTER Application May 11, 1935, Serial No. 20,972

12 Claims.

This invention relates to new and useful improvements in ultra-high-frequency radio transmitters.

It is the object of the present invention to produce an ultra-high-frequency transmitter of simple construction and one that will function at the predetermined frequency.

With this object in view according to one feature of the invention the filament of a vacuum tube oscillator forming part of the transmitter is connected with the source of filament current supply over bus bars insulatedly clamped together, a fixed connection being established between one of the bus bars and the transmitter shield, and a variable connection being established between the same bus bar and the shield intermediate said fixed connection and the point at which the bus bar is connected with the filament terminal. By means of this arrangement radio frequency currents are prevented from flowing into the filament supply leads.

According to another feature of the invention, the grid condenser of the oscillator consists of two plates, one of which is bodily attached to the tank circuit and the other to the clamp for the grid terminal.

The spacing between these plates may be varied and since the usual wires leading to the condenser plates are lacking, the inductive reactance of the condenser is reduced toa minimum.

According to another feature of the invention, the condenser elements of the tank circuit adjacent the vacuum tube oscillator are shaped closely to conform to the outlines of the glass vessel enclosing the vacuum tube oscillator, whereby inductive reactance is minimized.

Still another feature of the invention has to do with the combination in a unitary structure of a variable rotary grid condenser and a block- 40 ing condenser and the mounting of this unitary structure on the shell of the transmitter.

The invention may be'best understood by reference to the following description which sets forth the salient features of the same, reference 5 being made to the accompanying drawings in which:

Fig. 1 is a diagram of the electrical circuits of the ultra-high-frequency radio transmitter;

Figs. 2 and 3 show in side elevation andtrans- 50 verse cross-section, respectively, the constructional details of the filament transmission line;

Figs. 4 and 5 illustrate in top plan view and side elevation, respectively, the constructional details of the grid condenser; and

55 Fig. 6 shows in perspective the details of the mounting bracket for the grid tuning condenser, a portion. of which forms a blocking condenser.

Referring to Fig. 1, power for the filament l of a triode 2 is supplied from a 500-cyc1e source over a filament transmission line (later to be described 5 in detail in connection with Figs. 2 and 3), composed of parallel copper bus bars 3 and 4 separated by a mica insulator 5 inserted between the bus bars. The filament heating source may be, of course, of a different frequency, or of direct 10 current. The bus bar 3 is conductively connected by means of members 6 and I with a metal shield 8 surrounding the transmitter. Connecting member i is fixed adjacent to the point where the filament transmission line passes through the 15 metal shield 8, and is within said shield. The connecting member 6 is arranged to slide along the bus bar 3 in order to find a suitable point in relation to the point where member I is connected, for draining off the ultra-high-frequen- 20 cies which would otherwise penetrate into the filament power supply source. Bus bars 3 and 4 are connected to the filament l of the vacuum tube 2. In shunt to these bus bars are connected wires 9 and in which lead to a filament 5 voltmeter Ii having a by-pass condenser I2 connected across its terminals.

It should be noted that the arrangement of the filament of the transmission line performs all the functions of the transmission line shown and 30 described in our copending application Ser. No. 728,552 filed June 1, 1934, Patent No. 2,068,990, dated January 26, 1937. No separate condensers such as those shown in our copending application between the filament conductors and the surrounding shield need be provided in the present case since the capacitance between conducting bars 3 and 4 and the grounding of the latter affords sufficient protection against high frequency currents entering the filament supply. 40

The negative. bias for grid I3 of tube 2 is obtained from battery I4 through wire l5 which connects to a grid current meter l6, said meter having a by-pass condenser IT. The other side of the meter is connected by means of a wire l8 to 5 one side of a blocking condenser IS, the other side of which is shown as grounded. Actually this connection is made by means of a special mounting bracket which will be described in connection with Fig. 6. Wire l8 alsoconnects to one side of inductance coil 20 and adjustable condenser 2|. Coil 2B and condenser 2| together form an anti-resonant tuned circuit in series with the grid battery supply. The other sides of the coil and condenser are connected together, the common point being connected to the grid l3.

The high voltage for plate 22 of vacuum tube 2 is supplied. from a D. C. generator 23 through a vacuum key 390. and a high potential terminal 24 which is connected by wire 25 to one side of a voltage multiplier 26. The anode voltage supply source may, of course, be pulsating direct current or even alternating current. The other side of the voltage multiplier is connected by wire 2! to a grounded plate voltmeter 28 having a by-pass condenser 29. A wire 30 is connected to the same terminal of the voltage multiplier 26 as wire 25 and goes to one side of a radio frequency choke coil 3|, the function of which is to prevent the ultra-high-frequencies from flowing back into the high voltage supply circuit. The other side of coil 3| is connected to the midpoint 32 of a tank circuit. The tank circuit comprises a copper tube 33 on one half of which is mounted a copper dome 34 having flanges 35. These flanges are located in close proximity to similar flanges 35 attached to a similar copper dome 31 which is mounted on the other half of the copper tube 33. The domes 34 and 31 are mounted concentrically with the copper tube 33. One of said domes with its flanges is arranged to be adjustable about the axis of the copper tube. The details of this construction are described in a patent to Frederick A. Kolster, No. 2,031,490, issued February 18, 1936. The tank circuit is a parallel tuned circuit, the inductance of which is mainly due to the copper tube 33 in conjunction with the copper domes 34 and 31, and the capacity of which is mainly due to the flanges 35 and 36 forming the plates of condensers. This type of construction provides a parallel resonant circuit of extremely low effective resistance. One side of the tank circuit, i. e., the dome '34, is connected to the plate 22 of tube 2. The other side of the tank circuit, i. e., dome '31, is connected through a feed-back condenser 38 to the grid l 3 in a manner to be described in detail in connection with Figs. 4 and 5.

A DC. ammeter 39 having 'a'by-pass condenser 40 is connected over wires '4! and 42 in series with the high plate voltage supply 23. The

function of the ammeter is to measure the plate current.

The frequency'of the oscillations is determined mainly by the frequency of parallel resonance of the tank circuit which, as previously mentioned, has a very low effective resistance. The conditions for oscillation are obtained by adjustment of the condenser 2| whichforms a part of the parallel grid circuit in conjunction with the inter-electrode capacities of the tube 2. The ultra-high-frequency output circuit is electrostatically coupled by means of the copper rods 43 and 44 to the flanges 35 and 36 of the tank circuit. Said rods connect to insulated ultrahigh-frequency output terminals 45 and 46 with which the antenna is connected. Intermediate the point of coupling and said terminals an antiresonant circuit is connected in shunt between the copper rods. The anti-resonant circuit comprises an inductance coil 41 in parallel with adjustable condensers 48 and 49, said condensers being in series with each other. The coil 41 is inductively coupled to a coil 50, the terminals of which are connected to the heater terminals of a thermocouple'5l. The galvanometer terminals of said thermocouple are connected through radio frequency choke coils "52 to the terminals of a microammeter53'which has 'a by-p'ass o'ondenser 54. The last described arrangement provides means for measuring the ultra-high-frequency output current.

The construction details of the filament transmission line are shown in Figs. 2 and 3. Bus bar 4 is rectangular in cross-section being several times as wide as it is thick. Bus bar 3 is similar in shape except that it is slightly wider and is bevelled along the two upper edges. These two bus bars with the strip of mica 5 between are bolted together at points 60, 6|, 62 and 63 in such a manner that the bars are insulated from each other. Bar 3 is the longer of the two and extends beyond bar 4 at both ends. One end of bar 3 is supported by an insulating member 64 by means of a bolt and nut 65 which serves also as a terminal suitable for interconnecting this end of the bar 3 with one of the tube filament terminals. The other end of bar 3 is fastened to a copper block 66 which, in turn, is mounted on the metal shield 8. This forms the other terminal of bar 3 which is connected to one side of the source of filament current. The two terminals of bar 4 are shown at 61 and '68. Terminal 6'! is connected with the other filament terminal and 68 with the other side of the source of filament current. The sliding cop- 'per block 6 is illustrated in detail in Fig. 3.

Fig. '3 shows a cross-section taken through the assembly of Fig. 2at one of the bolting assemblies, say 6| of Fig. 2, looking toward the copper slide 6. Once the proper position is determined, the slide is bolted to the metal shield 8 by means of the screws and nuts 69, Ill. The upper part of the slide is shaped to receive the bolted assembly of bus bars 3 and 4 which is held firmly in place by the set screws 1| and 12 bearing against the bevelled'edges of the lower bus bar 3. The

bolting assembly consists of the flathead machine tion arises "from the desire to generate ultrahigh-frequencies, at which frequencies the inductive reactance even of short wires becomes appreciable. The presence of inductive reactance in this circuit influences the wavelength of the generatedoscillations to. make-it longer. In order to generate a wavelength as short as three meters, it has been found necessary to abolish as far as practicable the inductive reactance by making the plates of the condensers also serve as the conducting members, connecting one plate 38a of condenser-38 to'the flange 36 of the tank circuit andthe other plate 38bto the grid terminal l3 of the vacuum tube 2 as shown in Fig. 5.

Fig. 4 shows in detail the manner of constructing the grid condenser as seen from above. '31 is the upper or stationary part of the tank'oircuit,

and 36 one of its flanges (seen edgewise) to which is fastened by several screws metal plate 38a (also seen edgewise) fwhich forms one plate of the grid condenser '38. The other plate of the grid condenser is formed by'jmetal piece 381) which has its largest surface parallel to and a short distance away from, the plate 38a. The

edges of plate 381) areturned over'at right angles to tlie'inai'n face to"'give"the'plate mechanical 75 rigidity. One of the flanges thus formed is fastened at to a clamping plate 8|. This clamping plate is held against a plate guide 82 by means of a thumb nut assembly 83 which passes through the shield 8. The plate guide 82 is slotted horizontally where the thumb nut assembly 83 passes through, making it possible to slide the plate 8i to the left or right as far as the slot permits with the thumb nut loosened, the latter being tightened in the desired position. Thus the capacitance between plates 38a and 382) may be adjusted. The plate guide 82 is fastened to mounting strip 84 fastened to the shield 8 of the transmitter. Projecting through the mounting strip 84 is a metal clip 85 which receives the grid terminal of the vacuum tube 2. The clip 85 is fastened to and in metallic connection with the plate guide 82 and hence conductively connected with the plate 381) of the grid condenser.

As shown in Fig. 5, the edges of the condenser plates 38a and 3822- are beaded to give them mechanical strength. Ribbing 85 is provided, as shown, for the same purpose. Particular attention is called to the manner in which the shape of the condenser plates on the side 81 next to the vacuumtube 2 follows closely the outline 88 of the latter, reducing to a minimum the inductive reactance of the circuit.

Fig. 6 shows the details of the mounting bracket for the grid tuning condenser 2|, a portion of which forms a blocking condenser which serves to block the rotor of the grid tuning condenser to ground. In the circuit drawing of Fig. l, the grid tuning condenser is indicated by 2! and the blocking condenser by 19. Referring to Fig. 6, the grid tuning condenser 2| is in the form of an adjustable air condenser, the rotor shaft of which passes through a brass plate 98, a sheet of mica SI and the brass mounting bracket 92. The end of the rotor shaft is mechanically coupled by an insulating coupling 93 to a control shaft 94 which extends through the metal panel 8. The rotor shaft is in conductive connection only with the brass plate 96. The brass plate 9!], the mica dielectric 9! and the brass bracket 92 fastened together by the insulating screws 93' and 94' comprise the blocking condenser IS. The conductive connection to the front of the metal shield 8 or ground is made through the brass mounting bracket 92 which is not insulated therefrom. The advantage of this type of mounting lies in the very low value of inductance offered by the blocking condenser. Other types of blocking condensers introduce considerable inductive reactance at ultra-high frequencies because of relatively long wires used in connecting them into the circuits and the forms of the condensers.

What is claimed is:

1. In an ultra-high-frequency radio transmitter, a metal shield housing the transmitter, a vacuum tube oscillator having a filament, a source of filament current supply, a filament transmission line connecting said source with said filament, a fixed conductive connection between one side of the filament transmission line and said metal shield, and an adjustable conductive connection between said one side of the filament transmission line and the metal shield between the fixed connection and the terminal of said filament.

2. In an ultra-high-frequency radio transmitter, a metal shield housing the transmitter, a vacuum tube oscillator having a filament, a source of filament current supply, a filament transmission line consisting of two fiat bars separated by a layer of insulation connecting said source with said filament, a fixed conductive connection between one bar and said metal shield, and an adjustable conductive connection between said one bar and the metal shield between the fixed connection and the terminal of said filament.

3. An ultra-'high-frequency transmitter comprising a metal shield housing the transmitter, a vacuum tube oscillator having a filament, a source of filament current supply, a filament transmission line connecting said source with said filament comprising two bus bars clamped together and insulated from each other, an insulating mounting for one end of one of said bars on said metal shield, a conducting fixed mounting for the other end of said one of said bars on said metal shield, a conductive slider engaging said one of said bars, and means for fastening said slider to said metal shield intermediate said insulating and fixed mountings.

4. An ultra-high-frequency transmitter comprising a metal shield housing the transmitter, a vacuum tube oscillator having a filament, a source of filament current supply, a filament transmission line connecting said source with said filament comprising two copper bus bars clamped together and insulated from each other, one of said bars being substantially rectangular in cross-section, the other of said bars being slightly wider and longer and likewise substantially rectangular in cross-section except that two adjacent longitudinal edges are bevelled, an

insulating block attached to one end of said bevelled bar and supported by said metal shield, a copper block attached to the other end of said bevelled bar and supported by said metal shield, a second copper block with a portion cut out to receive said bars, and provided with set screws which bear against the bevelled surfaces of said bevelled bar, and means for fastening said second block to said metal shield.

5. In an ultra-high-frequency transmitter, an evacuated oscillator tube having a cathode, a grid and an anode, a tank circuit, a grid condenser having one plate attached to one side of the tank circuit and a second plate attached to the grid terminal of the oscillator tube, said condenser plates being disposed physically between the oscillator tube and the tank circuit and lying substantially in a plane which includes a straight line between said grid terminal and said tank circuit and being so shaped and of such area as to form substantially the entire conductive connections between said grid terminal and the tank circuit, whereby the inductive reactances due to the connections from the tank circuit and the grid to the plates of said condenser are both reduced to a minimum, and means for adjusting the spacing of said plates.

6. In an ultra-high-frequency transmitter, a shield enclosing said transmitter, an evacuated oscillator tube having a cathode, a grid and an anode, a tank circuit, a grid condenser having a rigid plate attached to one side of the tank circuit and a second rigid plate attached to the grid terminal of the oscillator tube, said condenser plates being disposed physically between the oscillator tube and the tank circuit and extending substantially in planes parallel to the axis of the oscillator tube and being so shaped and of such area as to form substantially the entire conductive connections between said grid terminal and the tank circuit, whereby inductive reactance due to the connections to the plates of said condenser is reduced to a minimum, and a removable clamp operable from outside of said shield for fastening said second plate to said shield adjustably with respect to the first plate.

'7. An ultra-high-frequency transmitter, a vacuum tube oscillator having a cathode, a grid and an anode enclosed within an evacuated vessel, a tank circuit, a grid condenser having one plate attached to a portion of said tank circuit adjacent to said vessel and a second plate attached to the grid terminal of said vessel, said condenser plates being disposed physically between the tank circuit and the oscillator tube in parallel planes in the general direction of a straight line between the tank circuit and the grid terminal and being so shaped that the edges thereof adjacent the oscillator tube conform substantially to the outline of and lying in close proximity to said vessel thereby to reduce to a minimum the inductive reactance due to a connection between the grid terminal and the tank circuit.

8. In an ultra-high-frequency transmitter, a grounded metal shield for the transmitter, a vacuum tube oscillator having a grid, a variable rotary condenser comprising a rotor and a stator insulated therefrom, a conductive connection from said stator to said grid, means for blocking the rotor of said condenser to ground comprising a mounting bracket of conducting material fastened to said shield, and a sheet of conducting material fastened to said bracket and insulated therefrom, the condenser rotor shaft passing through said sheet, bracket and shield and being conductively connected to said sheet.

9. In an ultra-high-frequency transmitter, a grounded metal shield for the transmitter, a vacuum tube oscillator having a grid, a variable rotary condenser comprising a rotor and a stator insulated therefrom, a conductive connection from said stator to said grid, means for blocking the rotor of said condenser to ground comprising a substantially U-shaped mounting bracket of conducting material fastened to said shield, a layer of insulation on said bracket, a sheet of conducting material on said layer of insulation, the condenser rotor shaft passing through said sheet, layer, bracket and shield, conductive connection between the rotor shaft and the sheet, and insulation between the rotor and the other parts through which it passes.

10. In an ultra-high-frequency radio transmitter, a metal shield for the transmitter, a vacuum tube oscillator having a filament, a source of filament current supply, a filament transmission line consisting of two conducting bars separated by a layer of insulating material connecting said source with said filament, means for so maintaining the fixed relation between the elements of said transmission line that said elements form a unitary structure and an adjustable conductive connection between one of said bars and the metal shield.

11. In an ultra-high-frequency radio transmitter, a vacuum tube oscillator having a cathode, a grid and an anode, a tank circuit mounted in proximity to said oscillator tube and comprising an inductor and a condenser connected in parallel and with the anode terminal of the oscillator tube positioned immediately below the tank circuit, a short connection from the anode terminal to the tank circuit, a grid condenser having one plate thereof attached to a plate of the tank circuit condenser and forming an extension thereof, a second plate for the grid condenser disposed substantially parallel to said one plate and attached to the grid terminal of the oscillator tube, the plates of said grid condenser being so shaped and of such area that the inductive reactance due to the connections between the tank circuit and the grid and anode terminals of the oscillator tube is reduced to a minimum.

12. In an ultra-high frequency radio transmitter, a vacuum tube oscillator having a cathode, a grid and an anode, a tank circuit mounted in proximity to said oscillator tube and comprising an inductor and a condenser connected in parallel and with the anode terminal of the oscillator tube positioned immediately below the tank circuit, a short connection from the anode terminal to the tank circuit, a grid condenser having one plate thereof attached to a plate ,of the tank circuit condenser and forming an extension thereof, a second plate for the grid condenser disposed substantially parallel to said one plate and attached to the grid terminalof the oscillator tube, the plates of said grid condenser being positioned physically between the tank circuit and the oscillator tube and of such shape and area as to occupy the space therebetween whereby the inductive reactance due to the connections from the tank circuit to the grid and anode terminals of the oscillator tube is reduced to a minimum.

FREDERICK A. KOLSTER. PAUL F. BYRNE. 

